RESEARCH FOR MECHANISM OF HOMOLOGOUS CHROMOSOMAL RECOMBINATION IN MOUSE MEIOSIS

在哺乳动物中，小鼠主要组织相容性复合体（MHC）是唯一的区域，其中减数分裂重组的断点在分子水平上进行了系统研究。在这个区域，减数分裂重组不是随机发生的，而是聚集在被称为热点的有限区域。到目前为止，该区域已确定了四个热点。某一DNA片段上热点的存在或不存在取决于遗传杂交中涉及的MHC单倍型。例如，在标准实验室单倍型之间的杂交中观察到Eb热点。在包括cas 3和wm 7单倍型的遗传杂交中，大多数重组发生在Lmp 2热点。Lmp 2和Eb热点已经在分子水平上得到了很好的表征。确定了这两个热点周围的序列，并分析了断裂点的精细位置。Lmp 2和Eb热点之间的序列比较揭示了几个常见的分子基序 ...更多信息 为了阐明这些基序在热点重组中的作用，并理解重组仅限于热点的机制，我们在分子水平上表征了其他热点。当在遗传杂交中使用野生小鼠衍生的cas 4单倍型时，减数分裂重组以高频率在Pb基因附近的热点处发生。这个热点的分子表征，指定铅热点，尚未完成。到目前为止，我们已经获得了6个独立的重组体在铅热点后，筛选600小鼠cas 4和wm 7单倍型之间的杂交产生。这些重组体的断裂点定位于Pb基因附近的15 kb DNA片段。在本研究中，我们试图对六个重组体的断裂点进行更完整的定位。首先，我们构建了包括断裂点的15 kb DNA片段的限制性内切酶图谱。随后，我们通过PCR-SSCP分析检测亲本DNA片段之间的多态性，确定了6个重组体中由15 kb DNA片段组成的几个短DNA片段的亲本来源。结果表明，在Pb基因3 '端附近的一段5 kb的DNA片段内，至少有5个重组体发生了重组，并测定了Pb热点附近的核苷酸序列。结果表明，该热点位于Pb基因的3 '端。因此，与芽殖酵母中的情况相比，小鼠MHC中表征的所有四个热点似乎都位于基因的3 '端或内含子。这一结果表明，在小鼠的热点减数分裂重组的分子机制是不同的芽殖酵母。少

In mammals, the murine major histocompatibility complex (MHC) is the only region where breakpoints of meiotic recombination are systematically studied at the molecular level. In this region, meiotic recombinations do not occur at random but are clustered in limited regions known as hotspots. Thus far, four hotspots have been identified in this region. The presence or absence of a hotspot on a certain DNA segment depends on the MHC haplotypes involved in genetic crosses. For example, the Eb hotspot is observed in crosses between standard laboratory haplotypes. In genetic crosses including cas3 and wm7 haplotypes which were derived from Asian wild mice, most of the recombinations occurred at the Lmp2 hotspot. Lmp2 and Eb hotspots have been well characterized at the molecular level. Sequences around these two hotspots were determined and the fine locations of the breakpoints were analyzed. Comparison of the sequences between Lmp2 and Eb hotspots revealed several molecular motifs commonly … More shared by the two hotspots.In order to elucidate the roles of these motifs in recombinations at the hotspots and to understand the mechanism by which recombinations are restricted to hotspots, we have characterize other hotspots at the molecular level. Meiotic recombination takes place at a high frequency at a hotspot in the vicinity of the Pb gene, when the wild mouse derived cas4 haplotype is used in the genetic cross. Molecular characterization of this hotspot, designated Pb hotspot, has not yet been done. So far, we have obtained six independent recombinants at the Pb hotspot after screening six hundred mice generated from crosses between cas4 and wm7 haplotypes. The breakpoints of these recombinants were localized to a 15 kb of DNA fragment in the vicinity of the Pb gene. In this study, we attempted to make a more complete map of the breakpoints of the six recombinants. First, we constructed the restriction map of the 15 kb of DNA fragment including the breakpoints. Subsequently, we determined the parental origins of several short DNA segments consisting of the 15 kb of DNA fragment in the six recombinants, by examining polymorphisms between parental DNA segments through PCR-SSCP analysis. At a result, at least five recombinations were found to be confined to a 5 kb of DNA segment located proximal to the 3'end of the Pb gene.We have determined nucleotide sequence around Pb hotspot. The result clearly indicated that the hotspot is located at 3'end of the Pb gene. Thus, it appeared that all four hotspots characterized in the mouse MHC are located at either 3'end or introns of genes, contrasting to the cases in budding yeast. The result suggests that molecular machinery operating in meiotic recombinations at the mouse hotspots is different from that in budding yeast. Less